This is not just a hypothetical question.  It is for a very real situation on a polymer weapon with a small ID plate.

If you Form 1 an SBR under a trust, and 2/3rds of your trust name is already engraved on the receiver, do you need to engrave it again?   Is there any requirement that the words of your trust name appear together, in sequence?

i.e..

Say I have a...  Keltec somethingorother with serial number SNxxx

My trust name is "Keltec SNxxx Trust"

"Keltec" and "SNxxx" are already engraved on the receiver somewhere

Does "Keltec SNxxx Trust" need to be engraved as a phrase?  

or could I just engrave "Trust" somewhere?

My opinion is to mark the full name of the trust.  The name of the trust should be clear by reading the engraving without having to guess or infer that some elements of the name are scattered in other locations around the receiver.  I generally use a reasonable person rule - would a reasonable person read your trust name and readily know the name of the trust?  The engraved name should match the name provided on the Form 1 (shown in box 3b of the 5320.1).

Since the Manufacturer is the "KelTec SNxxxx Trust" then "KelTec SNxxxx Trust" must appear on the firearm in that manner.  

By your logic, a manufacturer could engrave letters all over the receiver in random places and random order and someone would have to connect the dots in the crypto quiz to actually figure it out.  Same with the location that's required.  Info must be presented in a coherent manner and with certain physical requirements (size, depth, conspicuous location).

Now, at least in AL, the only requirement for the name of the Trust is that it must include the word "Trust".  I have engraved several items that were manufactured by the "In God We Trust" trust.  Looks like a statement, actually is the name.  I have one customer who's going to do a trust called the "Misplaced Trust".

lol, I like that.  Ok, so keep it together.  got it.